<!DOCTYPE html>
<html lang="en-US">
  <head>
    <meta charset="utf-8">
    <meta name="viewport" content="width=device-width,initial-scale=1">
    <title>泛型 | Keith&#39;s blog</title>
    <meta name="generator" content="VuePress 1.8.0">
    <link rel="icon" href="/img/favicon.png">
    <script data-ad-client="ca-pub-7828333725993554" async="async" src="https://pagead2.googlesyndication.com/pagead/js/adsbygoogle.js"></script>
    <meta name="description" content="web前端技术博客,简洁至上,专注web前端学习与总结。JavaScript,js,ES6,TypeScript,vue,python,css3,html5,Node,git,github等技术文章。">
    <meta name="keywords" content="前端博客,个人技术博客,前端,前端开发,前端框架,web前端,前端面试题,技术文档,学习,面试,JavaScript,js,ES6,TypeScript,vue,python,css3,html5,Node,git,github,markdown">
    <meta name="baidu-site-verification" content="7F55weZDDc">
    <meta name="theme-color" content="#11a8cd">
    <link rel="preload" href="/assets/css/0.styles.95a28cfa.css" as="style"><link rel="preload" href="/assets/js/app.ae5bf724.js" as="script"><link rel="preload" href="/assets/js/2.72b09a26.js" as="script"><link rel="preload" href="/assets/js/3.96877024.js" as="script"><link rel="preload" href="/assets/js/165.08b51ce6.js" as="script"><link rel="prefetch" href="/assets/js/10.3e431465.js"><link rel="prefetch" href="/assets/js/100.c7b84f24.js"><link rel="prefetch" href="/assets/js/101.e5a7e6f5.js"><link rel="prefetch" href="/assets/js/102.85992487.js"><link rel="prefetch" href="/assets/js/103.3f187c57.js"><link rel="prefetch" href="/assets/js/104.103d7471.js"><link rel="prefetch" href="/assets/js/105.df0063c0.js"><link rel="prefetch" href="/assets/js/106.d3f285ee.js"><link rel="prefetch" href="/assets/js/107.7ca5e73a.js"><link rel="prefetch" href="/assets/js/108.b5e1495a.js"><link rel="prefetch" href="/assets/js/109.12b39840.js"><link rel="prefetch" href="/assets/js/11.c0c2ac1e.js"><link rel="prefetch" href="/assets/js/110.2996b4eb.js"><link rel="prefetch" href="/assets/js/111.752c7e87.js"><link rel="prefetch" href="/assets/js/112.7c01a356.js"><link rel="prefetch" href="/assets/js/113.240fbeb5.js"><link rel="prefetch" href="/assets/js/114.502fae11.js"><link rel="prefetch" href="/assets/js/115.28ee11f8.js"><link rel="prefetch" href="/assets/js/116.a3f220c8.js"><link rel="prefetch" href="/assets/js/117.293dbd7c.js"><link rel="prefetch" href="/assets/js/118.7fe06c79.js"><link rel="prefetch" href="/assets/js/119.eb539041.js"><link rel="prefetch" href="/assets/js/12.0ea0beb2.js"><link rel="prefetch" href="/assets/js/120.8502bd78.js"><link rel="prefetch" href="/assets/js/121.696d358f.js"><link rel="prefetch" href="/assets/js/122.a629ef96.js"><link rel="prefetch" href="/assets/js/123.bc97cb45.js"><link rel="prefetch" href="/assets/js/124.e9dbc4a1.js"><link rel="prefetch" href="/assets/js/125.3372248a.js"><link rel="prefetch" href="/assets/js/126.58bf8057.js"><link rel="prefetch" href="/assets/js/127.532c80ac.js"><link rel="prefetch" href="/assets/js/128.a8a9dd63.js"><link rel="prefetch" href="/assets/js/129.952e36b7.js"><link rel="prefetch" href="/assets/js/13.81b38e3a.js"><link rel="prefetch" href="/assets/js/130.3f453493.js"><link rel="prefetch" href="/assets/js/131.15bb01bf.js"><link rel="prefetch" href="/assets/js/132.5e501da7.js"><link rel="prefetch" href="/assets/js/133.fbd296a8.js"><link rel="prefetch" href="/assets/js/134.a455c276.js"><link rel="prefetch" href="/assets/js/135.50985645.js"><link rel="prefetch" href="/assets/js/136.dd156bdc.js"><link rel="prefetch" href="/assets/js/137.91d77519.js"><link rel="prefetch" href="/assets/js/138.af96bbc9.js"><link rel="prefetch" href="/assets/js/139.ff60e390.js"><link rel="prefetch" href="/assets/js/14.13ff5f93.js"><link rel="prefetch" href="/assets/js/140.51ef13cd.js"><link rel="prefetch" href="/assets/js/141.2c36f0bb.js"><link rel="prefetch" href="/assets/js/142.745a5a9d.js"><link rel="prefetch" href="/assets/js/143.ef12ce5a.js"><link rel="prefetch" href="/assets/js/144.d53b8a10.js"><link rel="prefetch" href="/assets/js/145.01c80734.js"><link rel="prefetch" href="/assets/js/146.ff1abf8c.js"><link rel="prefetch" href="/assets/js/147.b334a956.js"><link rel="prefetch" href="/assets/js/148.82d1c504.js"><link rel="prefetch" href="/assets/js/149.4872ca41.js"><link rel="prefetch" href="/assets/js/15.ba6da9d5.js"><link rel="prefetch" href="/assets/js/150.eaa1b09e.js"><link rel="prefetch" href="/assets/js/151.b9deeab6.js"><link rel="prefetch" href="/assets/js/152.8914ff06.js"><link rel="prefetch" href="/assets/js/153.1c968910.js"><link rel="prefetch" href="/assets/js/154.ac2ac8e9.js"><link rel="prefetch" href="/assets/js/155.a41ac4d1.js"><link rel="prefetch" href="/assets/js/156.07ec7daa.js"><link rel="prefetch" href="/assets/js/157.d0cfaeb2.js"><link rel="prefetch" href="/assets/js/158.4a3844de.js"><link rel="prefetch" href="/assets/js/159.cd2739bf.js"><link rel="prefetch" href="/assets/js/16.bd936cd0.js"><link rel="prefetch" href="/assets/js/160.8ea34b7b.js"><link rel="prefetch" href="/assets/js/161.4bb2ece8.js"><link rel="prefetch" href="/assets/js/162.a4b2690b.js"><link rel="prefetch" href="/assets/js/163.85acbc57.js"><link rel="prefetch" href="/assets/js/164.acce92e2.js"><link rel="prefetch" href="/assets/js/166.7ad057e5.js"><link rel="prefetch" href="/assets/js/167.2d35a768.js"><link rel="prefetch" href="/assets/js/168.b7790709.js"><link rel="prefetch" href="/assets/js/169.11b5000c.js"><link rel="prefetch" href="/assets/js/17.1d7263eb.js"><link rel="prefetch" href="/assets/js/170.d93daf1f.js"><link rel="prefetch" href="/assets/js/171.14a45c02.js"><link rel="prefetch" href="/assets/js/172.c62eb70d.js"><link rel="prefetch" href="/assets/js/173.9dd4cb5e.js"><link rel="prefetch" href="/assets/js/174.deca226f.js"><link rel="prefetch" href="/assets/js/175.eef20df3.js"><link rel="prefetch" href="/assets/js/176.c09f5a25.js"><link rel="prefetch" href="/assets/js/177.99e3a6a8.js"><link rel="prefetch" href="/assets/js/178.22bd595d.js"><link rel="prefetch" href="/assets/js/179.ef63471d.js"><link rel="prefetch" href="/assets/js/18.9412ae71.js"><link rel="prefetch" href="/assets/js/180.306daca4.js"><link rel="prefetch" href="/assets/js/181.9f8eae15.js"><link rel="prefetch" href="/assets/js/182.36cd1ffa.js"><link rel="prefetch" href="/assets/js/183.0195ae23.js"><link rel="prefetch" href="/assets/js/184.61363002.js"><link rel="prefetch" href="/assets/js/185.d01ed7e5.js"><link rel="prefetch" href="/assets/js/186.915e1946.js"><link rel="prefetch" href="/assets/js/187.392993c9.js"><link rel="prefetch" href="/assets/js/188.afcb3c55.js"><link rel="prefetch" href="/assets/js/189.99313768.js"><link rel="prefetch" href="/assets/js/19.17a0f886.js"><link rel="prefetch" href="/assets/js/190.3740a1c8.js"><link rel="prefetch" href="/assets/js/191.a8cebbb8.js"><link rel="prefetch" href="/assets/js/192.a4e4b0eb.js"><link rel="prefetch" href="/assets/js/193.f87069af.js"><link rel="prefetch" href="/assets/js/194.a83aa1ad.js"><link rel="prefetch" href="/assets/js/195.6cccc323.js"><link rel="prefetch" href="/assets/js/196.0ca74fc2.js"><link rel="prefetch" href="/assets/js/197.e57085c4.js"><link rel="prefetch" href="/assets/js/198.9d8c4195.js"><link rel="prefetch" href="/assets/js/199.e34f6d16.js"><link rel="prefetch" href="/assets/js/20.751f715d.js"><link rel="prefetch" href="/assets/js/200.4f0c1baf.js"><link rel="prefetch" href="/assets/js/201.92b5153f.js"><link rel="prefetch" href="/assets/js/202.9f5b1117.js"><link rel="prefetch" href="/assets/js/203.84c5aa3f.js"><link rel="prefetch" href="/assets/js/204.950ec43f.js"><link rel="prefetch" href="/assets/js/205.3caa1fd5.js"><link rel="prefetch" href="/assets/js/206.c5d73eeb.js"><link rel="prefetch" href="/assets/js/207.f00a7726.js"><link rel="prefetch" href="/assets/js/208.49394867.js"><link rel="prefetch" href="/assets/js/209.f891c646.js"><link rel="prefetch" href="/assets/js/21.7e3b1dd6.js"><link rel="prefetch" href="/assets/js/210.9b3ce6fe.js"><link rel="prefetch" href="/assets/js/211.22cbc362.js"><link rel="prefetch" href="/assets/js/212.5380a60a.js"><link rel="prefetch" href="/assets/js/213.64691857.js"><link rel="prefetch" href="/assets/js/214.bf089249.js"><link rel="prefetch" href="/assets/js/215.285eccf0.js"><link rel="prefetch" href="/assets/js/216.e135c2e1.js"><link rel="prefetch" href="/assets/js/217.202ec57b.js"><link rel="prefetch" href="/assets/js/218.c1b5175f.js"><link rel="prefetch" href="/assets/js/219.ac0461eb.js"><link rel="prefetch" href="/assets/js/22.67350c09.js"><link rel="prefetch" href="/assets/js/220.944daf1d.js"><link rel="prefetch" href="/assets/js/221.73cba4fb.js"><link rel="prefetch" href="/assets/js/222.cd29efdd.js"><link rel="prefetch" href="/assets/js/223.5c40831a.js"><link rel="prefetch" href="/assets/js/224.0a05890e.js"><link rel="prefetch" href="/assets/js/225.7c20df0a.js"><link rel="prefetch" href="/assets/js/226.c7f69539.js"><link rel="prefetch" href="/assets/js/227.9ccb8852.js"><link rel="prefetch" href="/assets/js/228.77bd4f2e.js"><link rel="prefetch" href="/assets/js/229.1c656481.js"><link rel="prefetch" href="/assets/js/23.308ebe55.js"><link rel="prefetch" href="/assets/js/230.a3adae2f.js"><link rel="prefetch" href="/assets/js/231.f40d7e85.js"><link rel="prefetch" href="/assets/js/232.762cdd7e.js"><link rel="prefetch" href="/assets/js/233.29242686.js"><link rel="prefetch" href="/assets/js/24.2bb08ee4.js"><link rel="prefetch" href="/assets/js/25.3f1e32c9.js"><link rel="prefetch" href="/assets/js/26.6d06f7bc.js"><link rel="prefetch" href="/assets/js/27.edfd52de.js"><link rel="prefetch" href="/assets/js/28.8c959146.js"><link rel="prefetch" href="/assets/js/29.1621b6ed.js"><link rel="prefetch" href="/assets/js/30.751b1f17.js"><link rel="prefetch" href="/assets/js/31.ec665a74.js"><link rel="prefetch" href="/assets/js/32.1b1d72d5.js"><link rel="prefetch" href="/assets/js/33.b5bd40a4.js"><link rel="prefetch" href="/assets/js/34.2155b0a7.js"><link rel="prefetch" href="/assets/js/35.d59b534a.js"><link rel="prefetch" href="/assets/js/36.44a9c35e.js"><link rel="prefetch" href="/assets/js/37.fd11aa80.js"><link rel="prefetch" href="/assets/js/38.a788fd7b.js"><link rel="prefetch" href="/assets/js/39.0099a8f6.js"><link rel="prefetch" href="/assets/js/4.ff489266.js"><link rel="prefetch" href="/assets/js/40.40c37c27.js"><link rel="prefetch" href="/assets/js/41.a1008003.js"><link rel="prefetch" href="/assets/js/42.5b767b44.js"><link rel="prefetch" href="/assets/js/43.3f71078e.js"><link rel="prefetch" href="/assets/js/44.ad24f6c3.js"><link rel="prefetch" href="/assets/js/45.25e40b16.js"><link rel="prefetch" href="/assets/js/46.b64da983.js"><link rel="prefetch" href="/assets/js/47.17f22f05.js"><link rel="prefetch" href="/assets/js/48.98ac4a14.js"><link rel="prefetch" href="/assets/js/49.2d4cfb58.js"><link rel="prefetch" href="/assets/js/5.90f8b8b3.js"><link rel="prefetch" href="/assets/js/50.961c11a7.js"><link rel="prefetch" href="/assets/js/51.c69cd332.js"><link rel="prefetch" href="/assets/js/52.63e40184.js"><link rel="prefetch" href="/assets/js/53.ed393af3.js"><link rel="prefetch" href="/assets/js/54.e8bf699e.js"><link rel="prefetch" href="/assets/js/55.8c4b1f29.js"><link rel="prefetch" href="/assets/js/56.3ea6fad9.js"><link rel="prefetch" href="/assets/js/57.e355b934.js"><link rel="prefetch" href="/assets/js/58.591ee455.js"><link rel="prefetch" href="/assets/js/59.f75a544d.js"><link rel="prefetch" href="/assets/js/6.01e8382f.js"><link rel="prefetch" href="/assets/js/60.941e9812.js"><link rel="prefetch" href="/assets/js/61.4f56972b.js"><link rel="prefetch" href="/assets/js/62.bd0a67cc.js"><link rel="prefetch" href="/assets/js/63.5525dd5a.js"><link rel="prefetch" href="/assets/js/64.2e40b93d.js"><link rel="prefetch" href="/assets/js/65.7d7a1250.js"><link rel="prefetch" href="/assets/js/66.e88829f6.js"><link rel="prefetch" href="/assets/js/67.233ad823.js"><link rel="prefetch" href="/assets/js/68.037f0252.js"><link rel="prefetch" href="/assets/js/69.d5c49911.js"><link rel="prefetch" href="/assets/js/7.67b2aba3.js"><link rel="prefetch" href="/assets/js/70.039de8ef.js"><link rel="prefetch" href="/assets/js/71.fbbf266f.js"><link rel="prefetch" href="/assets/js/72.2cbdccb2.js"><link rel="prefetch" href="/assets/js/73.f824da30.js"><link rel="prefetch" href="/assets/js/74.c8e2bd49.js"><link rel="prefetch" href="/assets/js/75.2b326b41.js"><link rel="prefetch" href="/assets/js/76.6d52ed9a.js"><link rel="prefetch" href="/assets/js/77.6c219b3f.js"><link rel="prefetch" href="/assets/js/78.e3a6099c.js"><link rel="prefetch" href="/assets/js/79.847c1106.js"><link rel="prefetch" href="/assets/js/8.27cd446a.js"><link rel="prefetch" href="/assets/js/80.8fda2f41.js"><link rel="prefetch" href="/assets/js/81.c64976c1.js"><link rel="prefetch" href="/assets/js/82.44648201.js"><link rel="prefetch" href="/assets/js/83.a02ab71e.js"><link rel="prefetch" href="/assets/js/84.da4c143b.js"><link rel="prefetch" href="/assets/js/85.1e5083cb.js"><link rel="prefetch" href="/assets/js/86.373e4575.js"><link rel="prefetch" href="/assets/js/87.b7dae2d7.js"><link rel="prefetch" href="/assets/js/88.40e11959.js"><link rel="prefetch" href="/assets/js/89.711c7107.js"><link rel="prefetch" href="/assets/js/9.a4f4c6a7.js"><link rel="prefetch" href="/assets/js/90.36268f74.js"><link rel="prefetch" href="/assets/js/91.0b92ab60.js"><link rel="prefetch" href="/assets/js/92.9813b046.js"><link rel="prefetch" href="/assets/js/93.fcd128dd.js"><link rel="prefetch" href="/assets/js/94.c099f487.js"><link rel="prefetch" href="/assets/js/95.8042bfa3.js"><link rel="prefetch" href="/assets/js/96.45fc745f.js"><link rel="prefetch" href="/assets/js/97.32326e64.js"><link rel="prefetch" href="/assets/js/98.82035585.js"><link rel="prefetch" href="/assets/js/99.b24b3ac3.js">
    <link rel="stylesheet" href="/assets/css/0.styles.95a28cfa.css">
  </head>
  <body class="theme-mode-light">
    <div id="app" data-server-rendered="true"><div class="theme-container sidebar-open have-rightmenu have-body-img"><header class="navbar blur"><div title="目录" class="sidebar-button"><svg xmlns="http://www.w3.org/2000/svg" aria-hidden="true" role="img" viewBox="0 0 448 512" class="icon"><path fill="currentColor" d="M436 124H12c-6.627 0-12-5.373-12-12V80c0-6.627 5.373-12 12-12h424c6.627 0 12 5.373 12 12v32c0 6.627-5.373 12-12 12zm0 160H12c-6.627 0-12-5.373-12-12v-32c0-6.627 5.373-12 12-12h424c6.627 0 12 5.373 12 12v32c0 6.627-5.373 12-12 12zm0 160H12c-6.627 0-12-5.373-12-12v-32c0-6.627 5.373-12 12-12h424c6.627 0 12 5.373 12 12v32c0 6.627-5.373 12-12 12z"></path></svg></div> <a href="/" class="home-link router-link-active"><img src="/img/EB-logo.png" alt="Keith's blog" class="logo"> <span class="site-name can-hide">Keith's blog</span></a> <div class="links"><div class="search-box"><input aria-label="Search" autocomplete="off" spellcheck="false" value=""> <!----></div> <nav class="nav-links can-hide"><div class="nav-item"><a href="/" class="nav-link">首页</a></div><div class="nav-item"><a href="/pages/294b0a/" class="nav-link">个人总结</a></div><div class="nav-item"><div class="dropdown-wrapper"><button type="button" aria-label="来自大佬的文章" class="dropdown-title"><!----> <span class="title" style="display:;">来自大佬的文章</span> <span class="arrow right"></span></button> <ul class="nav-dropdown" style="display:none;"><li class="dropdown-item"><h4>前端</h4> <ul class="dropdown-subitem-wrapper"><li class="dropdown-subitem"><a href="/pages/8143cc480faf9a11/" class="nav-link">前端文章</a></li><li class="dropdown-subitem"><a href="/note/javascript/" class="nav-link">学习笔记</a></li></ul></li><li class="dropdown-item"><h4>页面</h4> <ul class="dropdown-subitem-wrapper"><li class="dropdown-subitem"><a href="/pages/8309a5b876fc95e3/" class="nav-link">HTML</a></li><li class="dropdown-subitem"><a href="/pages/0a83b083bdf257cb/" class="nav-link">CSS</a></li></ul></li><li class="dropdown-item"><h4>技术</h4> <ul class="dropdown-subitem-wrapper"><li class="dropdown-subitem"><a href="/pages/9a7ee40fc232253e/" class="nav-link">技术文档</a></li><li class="dropdown-subitem"><a href="/pages/4c778760be26d8b3/" class="nav-link">GitHub技巧</a></li><li class="dropdown-subitem"><a href="/pages/117708e0af7f0bd9/" class="nav-link">Nodejs</a></li><li class="dropdown-subitem"><a href="/pages/41f87d890d0a02af/" class="nav-link">博客搭建</a></li></ul></li><li class="dropdown-item"><h4>更多</h4> <ul class="dropdown-subitem-wrapper"><li class="dropdown-subitem"><a href="/pages/f2a556/" class="nav-link">学习</a></li><li class="dropdown-subitem"><a href="/pages/aea6571b7a8bae86/" class="nav-link">面试</a></li><li class="dropdown-subitem"><a href="/pages/2d615df9a36a98ed/" class="nav-link">心情杂货</a></li><li class="dropdown-subitem"><a href="/pages/baaa02/" class="nav-link">实用技巧</a></li></ul></li><li class="dropdown-item"><!----> <a href="/about/" class="nav-link">关于</a></li><li class="dropdown-item"><!----> <a href="/pages/beb6c0bd8a66cea6/" class="nav-link">收藏</a></li><li class="dropdown-item"><h4>索引</h4> <ul class="dropdown-subitem-wrapper"><li class="dropdown-subitem"><a href="/categories/" class="nav-link">分类</a></li><li class="dropdown-subitem"><a href="/tags/" class="nav-link">标签</a></li><li class="dropdown-subitem"><a href="/archives/" class="nav-link">归档</a></li></ul></li></ul></div></div> <a href="https://github.com/yangkeith/vuepress-theme-vdoing" target="_blank" rel="noopener noreferrer" class="repo-link">
    GitHub
    <span><svg xmlns="http://www.w3.org/2000/svg" aria-hidden="true" focusable="false" x="0px" y="0px" viewBox="0 0 100 100" width="15" height="15" class="icon outbound"><path fill="currentColor" d="M18.8,85.1h56l0,0c2.2,0,4-1.8,4-4v-32h-8v28h-48v-48h28v-8h-32l0,0c-2.2,0-4,1.8-4,4v56C14.8,83.3,16.6,85.1,18.8,85.1z"></path> <polygon fill="currentColor" points="45.7,48.7 51.3,54.3 77.2,28.5 77.2,37.2 85.2,37.2 85.2,14.9 62.8,14.9 62.8,22.9 71.5,22.9"></polygon></svg> <span class="sr-only">(opens new window)</span></span></a></nav></div></header> <div class="sidebar-mask"></div> <aside class="sidebar" style="display:none;"><div class="blogger"><img src="/img/avatar.jpg"> <div class="blogger-info"><h3>Keith</h3> <span>无名小卒</span></div></div> <nav class="nav-links"><div class="nav-item"><a href="/" class="nav-link">首页</a></div><div class="nav-item"><a href="/pages/294b0a/" class="nav-link">个人总结</a></div><div class="nav-item"><div class="dropdown-wrapper"><button type="button" aria-label="来自大佬的文章" class="dropdown-title"><!----> <span class="title" style="display:;">来自大佬的文章</span> <span class="arrow right"></span></button> <ul class="nav-dropdown" style="display:none;"><li class="dropdown-item"><h4>前端</h4> <ul class="dropdown-subitem-wrapper"><li class="dropdown-subitem"><a href="/pages/8143cc480faf9a11/" class="nav-link">前端文章</a></li><li class="dropdown-subitem"><a href="/note/javascript/" class="nav-link">学习笔记</a></li></ul></li><li class="dropdown-item"><h4>页面</h4> <ul class="dropdown-subitem-wrapper"><li class="dropdown-subitem"><a href="/pages/8309a5b876fc95e3/" class="nav-link">HTML</a></li><li class="dropdown-subitem"><a href="/pages/0a83b083bdf257cb/" class="nav-link">CSS</a></li></ul></li><li class="dropdown-item"><h4>技术</h4> <ul class="dropdown-subitem-wrapper"><li class="dropdown-subitem"><a href="/pages/9a7ee40fc232253e/" class="nav-link">技术文档</a></li><li class="dropdown-subitem"><a href="/pages/4c778760be26d8b3/" class="nav-link">GitHub技巧</a></li><li class="dropdown-subitem"><a href="/pages/117708e0af7f0bd9/" class="nav-link">Nodejs</a></li><li class="dropdown-subitem"><a href="/pages/41f87d890d0a02af/" class="nav-link">博客搭建</a></li></ul></li><li class="dropdown-item"><h4>更多</h4> <ul class="dropdown-subitem-wrapper"><li class="dropdown-subitem"><a href="/pages/f2a556/" class="nav-link">学习</a></li><li class="dropdown-subitem"><a href="/pages/aea6571b7a8bae86/" class="nav-link">面试</a></li><li class="dropdown-subitem"><a href="/pages/2d615df9a36a98ed/" class="nav-link">心情杂货</a></li><li class="dropdown-subitem"><a href="/pages/baaa02/" class="nav-link">实用技巧</a></li></ul></li><li class="dropdown-item"><!----> <a href="/about/" class="nav-link">关于</a></li><li class="dropdown-item"><!----> <a href="/pages/beb6c0bd8a66cea6/" class="nav-link">收藏</a></li><li class="dropdown-item"><h4>索引</h4> <ul class="dropdown-subitem-wrapper"><li class="dropdown-subitem"><a href="/categories/" class="nav-link">分类</a></li><li class="dropdown-subitem"><a href="/tags/" class="nav-link">标签</a></li><li class="dropdown-subitem"><a href="/archives/" class="nav-link">归档</a></li></ul></li></ul></div></div> <a href="https://github.com/yangkeith/vuepress-theme-vdoing" target="_blank" rel="noopener noreferrer" class="repo-link">
    GitHub
    <span><svg xmlns="http://www.w3.org/2000/svg" aria-hidden="true" focusable="false" x="0px" y="0px" viewBox="0 0 100 100" width="15" height="15" class="icon outbound"><path fill="currentColor" d="M18.8,85.1h56l0,0c2.2,0,4-1.8,4-4v-32h-8v28h-48v-48h28v-8h-32l0,0c-2.2,0-4,1.8-4,4v56C14.8,83.3,16.6,85.1,18.8,85.1z"></path> <polygon fill="currentColor" points="45.7,48.7 51.3,54.3 77.2,28.5 77.2,37.2 85.2,37.2 85.2,14.9 62.8,14.9 62.8,22.9 71.5,22.9"></polygon></svg> <span class="sr-only">(opens new window)</span></span></a></nav>  <ul class="sidebar-links"><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>初识 TypeScript</span> <span class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading open"><span>TypeScript 常用语法</span> <span class="arrow down"></span></p> <ul class="sidebar-links sidebar-group-items"><li><a href="/pages/28672e2743bbc3a7/" class="sidebar-link">基础类型</a></li><li><a href="/pages/54add7f5cf78088e/" class="sidebar-link">变量声明</a></li><li><a href="/pages/54ea89b497ec3bb3/" class="sidebar-link">接口</a></li><li><a href="/pages/fad060bd9a8bfac6/" class="sidebar-link">类</a></li><li><a href="/pages/870a51ba2a9edfad/" class="sidebar-link">函数</a></li><li><a href="/pages/8045759ec4ad3c01/" aria-current="page" class="active sidebar-link">泛型</a><ul class="sidebar-sub-headers"><li class="sidebar-sub-header"><a href="/pages/8045759ec4ad3c01/#基础示例" class="sidebar-link">基础示例</a></li><li class="sidebar-sub-header"><a href="/pages/8045759ec4ad3c01/#使用泛型变量" class="sidebar-link">使用泛型变量</a></li><li class="sidebar-sub-header"><a href="/pages/8045759ec4ad3c01/#泛型类型" class="sidebar-link">泛型类型</a></li><li class="sidebar-sub-header"><a href="/pages/8045759ec4ad3c01/#泛型类" class="sidebar-link">泛型类</a></li><li class="sidebar-sub-header"><a href="/pages/8045759ec4ad3c01/#泛型约束" class="sidebar-link">泛型约束</a><ul class="sidebar-sub-headers"><li class="sidebar-sub-header"><a href="/pages/8045759ec4ad3c01/#在泛型约束中使用类型参数" class="sidebar-link">在泛型约束中使用类型参数</a></li></ul></li></ul></li><li><a href="/pages/7279420c899c505d/" class="sidebar-link">类型推断</a></li><li><a href="/pages/3fb6c2f52ab398e3/" class="sidebar-link">高级类型</a></li></ul></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>ts-axios 项目初始化</span> <span class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>ts-axios 基础功能实现</span> <span class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>ts-axios 异常情况处理</span> <span class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>ts-axios 接口扩展</span> <span class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>ts-axios 拦截器实现</span> <span class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>ts-axios 配置化实现</span> <span class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>ts-axios 取消功能实现</span> <span class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>ts-axios 更多功能实现</span> <span class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>ts-axios 单元测试</span> <span class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>ts-axios 部署与发布</span> <span class="arrow right"></span></p> <!----></section></li></ul> <div class="sidebar-slot sidebar-slot-bottom"><!-- 正方形 -->
      <ins class="adsbygoogle"
          style="display:block"
          data-ad-client="ca-pub-7828333725993554"
          data-ad-slot="3508773082"
          data-ad-format="auto"
          data-full-width-responsive="true"></ins>
      <script>
          (adsbygoogle = window.adsbygoogle || []).push({});
      </script></div></aside> <div><main class="page"><div class="theme-vdoing-wrapper "><div class="articleInfo-wrap" data-v-70a2d273><div class="articleInfo" data-v-70a2d273><ul class="breadcrumbs" data-v-70a2d273><li data-v-70a2d273><a href="/" title="首页" class="iconfont icon-home router-link-active" data-v-70a2d273></a></li> <li data-v-70a2d273><a href="/note/typescript-axios" title="《TypeScript 从零实现 axios》-目录页" data-v-70a2d273>《TypeScript 从零实现 axios》</a></li> <li data-v-70a2d273><a href="/note/typescript-axios/#TypeScript 常用语法" title="《TypeScript 从零实现 axios》#TypeScript 常用语法" data-v-70a2d273>TypeScript 常用语法</a></li> <!----></ul> <div class="info" data-v-70a2d273><div title="作者" class="author iconfont icon-touxiang" data-v-70a2d273><a href="javascript:;" data-v-70a2d273>HuangYi</a></div> <div title="创建时间" class="date iconfont icon-riqi" data-v-70a2d273><a href="javascript:;" data-v-70a2d273>2020-01-05</a></div> <!----></div></div></div> <!----> <div class="content-wrapper"><div class="right-menu-wrapper"><div class="right-menu-margin"><div class="right-menu-content"></div></div></div> <h1><img src="">
          泛型
        </h1> <div class="page-slot page-slot-top"><!-- 固定100% * 90px可显示，max-height:90px未见显示-->
     <ins class="adsbygoogle"
          style="display:inline-block;width:100%;max-height:90px"
          data-ad-client="ca-pub-7828333725993554"
          data-ad-slot="6625304284"></ins>
      <script>
          (adsbygoogle = window.adsbygoogle || []).push({});
      </script></div> <div class="theme-vdoing-content content__default"><h1 id="泛型"><a href="#泛型" class="header-anchor">#</a> 泛型</h1> <p>软件工程中，我们不仅要创建定义良好且一致的 API，同时也要考虑可重用性。 组件不仅能够支持当前的数据类型，同时也能支持未来的数据类型，这在创建大型系统时为你提供了十分灵活的功能。</p> <p>在像 C# 和 Java 这样的语言中，可以使用泛型来创建可重用的组件，一个组件可以支持多种类型的数据。 这样用户就可以以自己的数据类型来使用组件。</p> <h2 id="基础示例"><a href="#基础示例" class="header-anchor">#</a> 基础示例</h2> <p>下面来创建第一个使用泛型的例子：<code>identity</code> 函数。 这个函数会返回任何传入它的值。 你可以把这个函数当成是 <code>echo</code> 命令。</p> <p>不用泛型的话，这个函数可能是下面这样：</p> <div class="language-typescript line-numbers-mode"><pre class="language-typescript"><code><span class="token keyword">function</span> <span class="token function">identity</span><span class="token punctuation">(</span>arg<span class="token operator">:</span> <span class="token builtin">number</span><span class="token punctuation">)</span><span class="token operator">:</span> <span class="token builtin">number</span> <span class="token punctuation">{</span>
  <span class="token keyword">return</span> arg
<span class="token punctuation">}</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br></div></div><p>或者，我们使用 <code>any</code> 类型来定义函数：</p> <div class="language-typescript line-numbers-mode"><pre class="language-typescript"><code><span class="token keyword">function</span> <span class="token function">identity</span><span class="token punctuation">(</span>arg<span class="token operator">:</span> <span class="token builtin">any</span><span class="token punctuation">)</span><span class="token operator">:</span> <span class="token builtin">any</span> <span class="token punctuation">{</span>
  <span class="token keyword">return</span> arg
<span class="token punctuation">}</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br></div></div><p>使用 <code>any</code> 类型会导致这个函数可以接收任何类型的 <code>arg</code> 参数，但是这样就丢失了一些信息：传入的类型与返回的类型应该是相同的。如果我们传入一个数字，我们只知道任何类型的值都有可能被返回。</p> <p>因此，我们需要一种方法使返回值的类型与传入参数的类型是相同的。这里，我们使用了<em>类型变量</em>，它是一种特殊的变量，只用于表示类型而不是值。</p> <div class="language-typescript line-numbers-mode"><pre class="language-typescript"><code><span class="token keyword">function</span> <span class="token generic-function"><span class="token function">identity</span><span class="token generic class-name"><span class="token operator">&lt;</span><span class="token constant">T</span><span class="token operator">&gt;</span></span></span><span class="token punctuation">(</span>arg<span class="token operator">:</span> <span class="token constant">T</span><span class="token punctuation">)</span><span class="token operator">:</span> <span class="token constant">T</span> <span class="token punctuation">{</span>
  <span class="token keyword">return</span> arg
<span class="token punctuation">}</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br></div></div><p>我们给 <code>identity</code> 添加了类型变量 <code>T</code>。 <code>T</code> 帮助我们捕获用户传入的类型（比如：<code>number</code>），之后我们就可以使用这个类型。 之后我们再次使用了 <code>T</code> 当做返回值类型。现在我们可以知道参数类型与返回值类型是相同的了。这允许我们跟踪函数里使用的类型的信息。</p> <p>我们把这个版本的 <code>identity</code> 函数叫做泛型，因为它可以适用于多个类型。 不同于使用 <code>any</code>，它不会丢失信息，像第一个例子那像保持准确性，传入数值类型并返回数值类型。</p> <p>我们定义了泛型函数后，可以用两种方法使用。 第一种是，传入所有的参数，包含类型参数：</p> <div class="language-typescript line-numbers-mode"><pre class="language-typescript"><code><span class="token keyword">let</span> output <span class="token operator">=</span> <span class="token generic-function"><span class="token function">identity</span><span class="token generic class-name"><span class="token operator">&lt;</span><span class="token builtin">string</span><span class="token operator">&gt;</span></span></span><span class="token punctuation">(</span><span class="token string">'myString'</span><span class="token punctuation">)</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br></div></div><p>这里我们明确的指定了 <code>T</code> 是 <code>string</code> 类型，并做为一个参数传给函数，使用了 <code>&lt;&gt;</code> 括起来而不是 <code>()</code>。</p> <p>第二种方法更普遍。利用了<em>类型推论</em> -- 即编译器会根据传入的参数自动地帮助我们确定 <code>T</code> 的类型：</p> <div class="language-typescript line-numbers-mode"><pre class="language-typescript"><code><span class="token keyword">let</span> output <span class="token operator">=</span> <span class="token function">identity</span><span class="token punctuation">(</span><span class="token string">'myString'</span><span class="token punctuation">)</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br></div></div><p>注意我们没必要使用尖括号（<code>&lt;&gt;</code>）来明确地传入类型；编译器可以查看 <code>myString</code> 的值，然后把 <code>T</code> 设置为它的类型。 类型推论帮助我们保持代码精简和高可读性。如果编译器不能够自动地推断出类型的话，只能像上面那样明确的传入 <code>T</code> 的类型，在一些复杂的情况下，这是可能出现的。</p> <h2 id="使用泛型变量"><a href="#使用泛型变量" class="header-anchor">#</a> 使用泛型变量</h2> <p>使用泛型创建像 <code>identity</code> 这样的泛型函数时，编译器要求你在函数体必须正确的使用这个通用的类型。 换句话说，你必须把这些参数当做是任意或所有类型。</p> <p>看下之前 <code>identity</code> 例子：</p> <div class="language-typescript line-numbers-mode"><pre class="language-typescript"><code><span class="token keyword">function</span> <span class="token generic-function"><span class="token function">identity</span><span class="token generic class-name"><span class="token operator">&lt;</span><span class="token constant">T</span><span class="token operator">&gt;</span></span></span><span class="token punctuation">(</span>arg<span class="token operator">:</span> <span class="token constant">T</span><span class="token punctuation">)</span><span class="token operator">:</span> <span class="token constant">T</span> <span class="token punctuation">{</span>
  <span class="token keyword">return</span> arg
<span class="token punctuation">}</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br></div></div><p>如果我们想打印出 <code>arg</code> 的长度。 我们很可能会这样做：</p> <div class="language-typescript line-numbers-mode"><pre class="language-typescript"><code><span class="token keyword">function</span> <span class="token generic-function"><span class="token function">loggingIdentity</span><span class="token generic class-name"><span class="token operator">&lt;</span><span class="token constant">T</span><span class="token operator">&gt;</span></span></span><span class="token punctuation">(</span>arg<span class="token operator">:</span> <span class="token constant">T</span><span class="token punctuation">)</span><span class="token operator">:</span> <span class="token constant">T</span> <span class="token punctuation">{</span>
  <span class="token builtin">console</span><span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span>arg<span class="token punctuation">.</span>length<span class="token punctuation">)</span>
  <span class="token keyword">return</span> arg
<span class="token punctuation">}</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br></div></div><p>如果这么做，编译器会报错说我们使用了 <code>arg</code> 的 <code>.length</code> 属性，但是没有地方指明 <code>arg</code> 具有这个属性。记住，这些类型变量代表的是任意类型，所以使用这个函数的人可能传入的是个数字，而数字是没有 <code>.length</code> 属性的。</p> <p>现在假设我们想操作 <code>T</code> 类型的数组而不直接是 <code>T</code>。由于我们操作的是数组，所以 <code>.length</code> 属性是应该存在的。我们可以像创建其它数组一样创建这个数组：</p> <div class="language-typescript line-numbers-mode"><pre class="language-typescript"><code><span class="token keyword">function</span> <span class="token generic-function"><span class="token function">loggingIdentity</span><span class="token generic class-name"><span class="token operator">&lt;</span><span class="token constant">T</span><span class="token operator">&gt;</span></span></span><span class="token punctuation">(</span>arg<span class="token operator">:</span> <span class="token constant">T</span><span class="token punctuation">[</span><span class="token punctuation">]</span><span class="token punctuation">)</span><span class="token operator">:</span> <span class="token constant">T</span><span class="token punctuation">[</span><span class="token punctuation">]</span> <span class="token punctuation">{</span>
  <span class="token builtin">console</span><span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span>arg<span class="token punctuation">.</span>length<span class="token punctuation">)</span>
  <span class="token keyword">return</span> arg
<span class="token punctuation">}</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br></div></div><p>你可以这样理解 <code>loggingIdentity</code> 的类型：泛型函数 <code>loggingIdentity</code>，接收类型参数 <code>T</code> 和参数 <code>arg</code>，它是个元素类型是 <code>T</code> 的数组，并返回元素类型是<code>T</code> 的数组。 如果我们传入数字数组，将返回一个数字数组，因为此时 <code>T</code> 的的类型为 <code>number</code>。 这可以让我们把泛型变量 <code>T</code> 当做类型的一部分使用，而不是整个类型，增加了灵活性。</p> <h2 id="泛型类型"><a href="#泛型类型" class="header-anchor">#</a> 泛型类型</h2> <p>上一节，我们创建了 <code>identity</code> 通用函数，可以适用于不同的类型。 在这节，我们研究一下函数本身的类型，以及如何创建泛型接口。</p> <p>泛型函数的类型与非泛型函数的类型没什么不同，只是有一个类型参数在最前面，像函数声明一样：</p> <div class="language-typescript line-numbers-mode"><pre class="language-typescript"><code><span class="token keyword">function</span> <span class="token generic-function"><span class="token function">identity</span><span class="token generic class-name"><span class="token operator">&lt;</span><span class="token constant">T</span><span class="token operator">&gt;</span></span></span><span class="token punctuation">(</span>arg<span class="token operator">:</span> <span class="token constant">T</span><span class="token punctuation">)</span><span class="token operator">:</span> <span class="token constant">T</span> <span class="token punctuation">{</span>
  <span class="token keyword">return</span> arg
<span class="token punctuation">}</span>

<span class="token keyword">let</span> myIdentity<span class="token operator">:</span> <span class="token operator">&lt;</span><span class="token constant">T</span><span class="token operator">&gt;</span><span class="token punctuation">(</span>arg<span class="token operator">:</span> <span class="token constant">T</span><span class="token punctuation">)</span> <span class="token operator">=&gt;</span> <span class="token constant">T</span> <span class="token operator">=</span> identity
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br></div></div><p>我们也可以使用不同的泛型参数名，只要在数量上和使用方式上能对应上就可以。</p> <div class="language-typescript line-numbers-mode"><pre class="language-typescript"><code><span class="token keyword">function</span> <span class="token generic-function"><span class="token function">identity</span><span class="token generic class-name"><span class="token operator">&lt;</span><span class="token constant">T</span><span class="token operator">&gt;</span></span></span><span class="token punctuation">(</span>arg<span class="token operator">:</span> <span class="token constant">T</span><span class="token punctuation">)</span><span class="token operator">:</span> <span class="token constant">T</span> <span class="token punctuation">{</span>
  <span class="token keyword">return</span> arg
<span class="token punctuation">}</span>

<span class="token keyword">let</span> myIdentity<span class="token operator">:</span> <span class="token operator">&lt;</span><span class="token constant">U</span><span class="token operator">&gt;</span><span class="token punctuation">(</span>arg<span class="token operator">:</span> <span class="token constant">U</span><span class="token punctuation">)</span> <span class="token operator">=&gt;</span> <span class="token constant">U</span> <span class="token operator">=</span> identity
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br></div></div><p>我们还可以使用带有调用签名的对象字面量来定义泛型函数：</p> <div class="language-typescript line-numbers-mode"><pre class="language-typescript"><code><span class="token keyword">function</span> <span class="token generic-function"><span class="token function">identity</span><span class="token generic class-name"><span class="token operator">&lt;</span><span class="token constant">T</span><span class="token operator">&gt;</span></span></span><span class="token punctuation">(</span>arg<span class="token operator">:</span> <span class="token constant">T</span><span class="token punctuation">)</span><span class="token operator">:</span> <span class="token constant">T</span> <span class="token punctuation">{</span>
  <span class="token keyword">return</span> arg
<span class="token punctuation">}</span>

<span class="token keyword">let</span> myIdentity<span class="token operator">:</span> <span class="token punctuation">{</span><span class="token operator">&lt;</span><span class="token constant">T</span><span class="token operator">&gt;</span><span class="token punctuation">(</span>arg<span class="token operator">:</span> <span class="token constant">T</span><span class="token punctuation">)</span><span class="token operator">:</span> <span class="token constant">T</span><span class="token punctuation">}</span> <span class="token operator">=</span> identity
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br></div></div><p>这引导我们去写第一个泛型接口了。我们把上面例子里的对象字面量拿出来做为一个接口：</p> <div class="language-typescript line-numbers-mode"><pre class="language-typescript"><code><span class="token keyword">interface</span> <span class="token class-name">GenericIdentityFn</span> <span class="token punctuation">{</span>
  <span class="token operator">&lt;</span><span class="token constant">T</span><span class="token operator">&gt;</span><span class="token punctuation">(</span>arg<span class="token operator">:</span> <span class="token constant">T</span><span class="token punctuation">)</span><span class="token operator">:</span> <span class="token constant">T</span>
<span class="token punctuation">}</span>

<span class="token keyword">function</span> <span class="token generic-function"><span class="token function">identity</span><span class="token generic class-name"><span class="token operator">&lt;</span><span class="token constant">T</span><span class="token operator">&gt;</span></span></span><span class="token punctuation">(</span>arg<span class="token operator">:</span> <span class="token constant">T</span><span class="token punctuation">)</span><span class="token operator">:</span> <span class="token constant">T</span> <span class="token punctuation">{</span>
  <span class="token keyword">return</span> arg
<span class="token punctuation">}</span>

<span class="token keyword">let</span> myIdentity<span class="token operator">:</span> GenericIdentityFn <span class="token operator">=</span> identity
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br></div></div><p>我们甚至可以把泛型参数当作整个接口的一个参数。 这样我们就能清楚的知道使用的具体是哪个泛型类型（比如： <code>Dictionary&lt;string&gt;</code> 而不只是<code>Dictionary</code>）。这样接口里的其它成员也能知道这个参数的类型了。</p> <div class="language-typescript line-numbers-mode"><pre class="language-typescript"><code><span class="token keyword">interface</span> <span class="token class-name">GenericIdentityFn<span class="token operator">&lt;</span><span class="token constant">T</span><span class="token operator">&gt;</span></span> <span class="token punctuation">{</span>
  <span class="token punctuation">(</span>arg<span class="token operator">:</span> <span class="token constant">T</span><span class="token punctuation">)</span><span class="token operator">:</span> <span class="token constant">T</span>
<span class="token punctuation">}</span>

<span class="token keyword">function</span> <span class="token generic-function"><span class="token function">identity</span><span class="token generic class-name"><span class="token operator">&lt;</span><span class="token constant">T</span><span class="token operator">&gt;</span></span></span><span class="token punctuation">(</span>arg<span class="token operator">:</span> <span class="token constant">T</span><span class="token punctuation">)</span><span class="token operator">:</span> <span class="token constant">T</span> <span class="token punctuation">{</span>
  <span class="token keyword">return</span> arg
<span class="token punctuation">}</span>

<span class="token keyword">let</span> myIdentity<span class="token operator">:</span> GenericIdentityFn<span class="token operator">&lt;</span><span class="token builtin">number</span><span class="token operator">&gt;</span> <span class="token operator">=</span> identity
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br></div></div><p>注意，我们的示例做了少许改动。 不再描述泛型函数，而是把非泛型函数签名作为泛型类型一部分。 当我们使用 <code>GenericIdentityFn</code> 的时候，还得传入一个类型参数来指定泛型类型（这里是：<code>number</code>），锁定了之后代码里使用的类型。对于描述哪部分类型属于泛型部分来说，理解何时把参数放在调用签名里和何时放在接口上是很有帮助的。</p> <p>除了泛型接口，我们还可以创建泛型类。 注意，无法创建泛型枚举和泛型命名空间。</p> <h2 id="泛型类"><a href="#泛型类" class="header-anchor">#</a> 泛型类</h2> <p>泛型类看上去与泛型接口差不多。 泛型类使用（ <code>&lt;&gt;</code>）括起泛型类型，跟在类名后面。</p> <div class="language-typescript line-numbers-mode"><pre class="language-typescript"><code><span class="token keyword">class</span> <span class="token class-name">GenericNumber<span class="token operator">&lt;</span><span class="token constant">T</span><span class="token operator">&gt;</span></span> <span class="token punctuation">{</span>
  zeroValue<span class="token operator">:</span> <span class="token constant">T</span>
  <span class="token function-variable function">add</span><span class="token operator">:</span> <span class="token punctuation">(</span>x<span class="token operator">:</span> <span class="token constant">T</span><span class="token punctuation">,</span> y<span class="token operator">:</span> <span class="token constant">T</span><span class="token punctuation">)</span> <span class="token operator">=&gt;</span> <span class="token constant">T</span>
<span class="token punctuation">}</span>

<span class="token keyword">let</span> myGenericNumber <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">GenericNumber<span class="token operator">&lt;</span><span class="token builtin">number</span><span class="token operator">&gt;</span></span><span class="token punctuation">(</span><span class="token punctuation">)</span>
myGenericNumber<span class="token punctuation">.</span>zeroValue <span class="token operator">=</span> <span class="token number">0</span>
myGenericNumber<span class="token punctuation">.</span><span class="token function-variable function">add</span> <span class="token operator">=</span> <span class="token keyword">function</span><span class="token punctuation">(</span>x<span class="token punctuation">,</span> y<span class="token punctuation">)</span> <span class="token punctuation">{</span>
  <span class="token keyword">return</span> x <span class="token operator">+</span> y
<span class="token punctuation">}</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br></div></div><p><code>GenericNumber</code> 类的使用是十分直观的，并且你可能已经注意到了，没有什么去限制它只能使用 <code>number</code> 类型。 也可以使用字符串或其它更复杂的类型。</p> <div class="language-typescript line-numbers-mode"><pre class="language-typescript"><code><span class="token keyword">let</span> stringNumeric <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">GenericNumber<span class="token operator">&lt;</span><span class="token builtin">string</span><span class="token operator">&gt;</span></span><span class="token punctuation">(</span><span class="token punctuation">)</span>
stringNumeric<span class="token punctuation">.</span>zeroValue <span class="token operator">=</span> <span class="token string">''</span>
stringNumeric<span class="token punctuation">.</span><span class="token function-variable function">add</span> <span class="token operator">=</span> <span class="token keyword">function</span><span class="token punctuation">(</span>x<span class="token punctuation">,</span> y<span class="token punctuation">)</span> <span class="token punctuation">{</span>
  <span class="token keyword">return</span> x <span class="token operator">+</span> y
<span class="token punctuation">}</span>

<span class="token builtin">console</span><span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span>stringNumeric<span class="token punctuation">.</span><span class="token function">add</span><span class="token punctuation">(</span>stringNumeric<span class="token punctuation">.</span>zeroValue<span class="token punctuation">,</span> <span class="token string">'test'</span><span class="token punctuation">)</span><span class="token punctuation">)</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br></div></div><p>与接口一样，直接把泛型类型放在类后面，可以帮助我们确认类的所有属性都在使用相同的类型。</p> <p>我们在<a href="/chapter2/class">类</a>那节说过，类有两部分：静态部分和实例部分。 泛型类指的是实例部分的类型，所以类的静态属性不能使用这个泛型类型。</p> <h2 id="泛型约束"><a href="#泛型约束" class="header-anchor">#</a> 泛型约束</h2> <p>我们有时候想操作某类型的一组值，并且我们知道这组值具有什么样的属性。在 <code>loggingIdentity</code> 例子中，我们想访问 <code>arg</code> 的 <code>length</code> 属性，但是编译器并不能证明每种类型都有 <code>length</code> 属性，所以就报错了。</p> <div class="language-typescript line-numbers-mode"><pre class="language-typescript"><code><span class="token keyword">function</span> <span class="token generic-function"><span class="token function">loggingIdentity</span><span class="token generic class-name"><span class="token operator">&lt;</span><span class="token constant">T</span><span class="token operator">&gt;</span></span></span><span class="token punctuation">(</span>arg<span class="token operator">:</span> <span class="token constant">T</span><span class="token punctuation">)</span><span class="token operator">:</span> <span class="token constant">T</span> <span class="token punctuation">{</span>
  <span class="token builtin">console</span><span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span>arg<span class="token punctuation">.</span>length<span class="token punctuation">)</span>
  <span class="token keyword">return</span> arg
<span class="token punctuation">}</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br></div></div><p>相比于操作 <code>any</code> 所有类型，我们想要限制函数去处理任意带有 <code>.length</code> 属性的所有类型。 只要传入的类型有这个属性，我们就允许，就是说至少包含这一属性。为此，我们需要列出对于 <code>T</code> 的约束要求。</p> <p>我们定义一个接口来描述约束条件，创建一个包含 <code>.length</code> 属性的接口，使用这个接口和 <code>extends</code> 关键字来实现约束：</p> <div class="language-typescript line-numbers-mode"><pre class="language-typescript"><code><span class="token keyword">interface</span> <span class="token class-name">Lengthwise</span> <span class="token punctuation">{</span>
  length<span class="token operator">:</span> <span class="token builtin">number</span>
<span class="token punctuation">}</span>

<span class="token keyword">function</span> <span class="token generic-function"><span class="token function">loggingIdentity</span><span class="token generic class-name"><span class="token operator">&lt;</span><span class="token constant">T</span> <span class="token keyword">extends</span> Lengthwise<span class="token operator">&gt;</span></span></span><span class="token punctuation">(</span>arg<span class="token operator">:</span> <span class="token constant">T</span><span class="token punctuation">)</span><span class="token operator">:</span> <span class="token constant">T</span> <span class="token punctuation">{</span>
  <span class="token builtin">console</span><span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span>arg<span class="token punctuation">.</span>length<span class="token punctuation">)</span> <span class="token comment">// OK</span>
  <span class="token keyword">return</span> arg
<span class="token punctuation">}</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br></div></div><p>现在这个泛型函数被定义了约束，因此它不再是适用于任意类型：</p> <div class="language-typescript line-numbers-mode"><pre class="language-typescript"><code><span class="token function">loggingIdentity</span><span class="token punctuation">(</span><span class="token number">3</span><span class="token punctuation">)</span><span class="token punctuation">;</span>  <span class="token comment">// Error</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br></div></div><p>我们需要传入符合约束类型的值，必须包含必须的属性：</p> <div class="language-typescript line-numbers-mode"><pre class="language-typescript"><code><span class="token function">loggingIdentity</span><span class="token punctuation">(</span><span class="token punctuation">{</span>length<span class="token operator">:</span> <span class="token number">10</span><span class="token punctuation">,</span> value<span class="token operator">:</span> <span class="token number">3</span><span class="token punctuation">}</span><span class="token punctuation">)</span> <span class="token comment">// OK</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br></div></div><h3 id="在泛型约束中使用类型参数"><a href="#在泛型约束中使用类型参数" class="header-anchor">#</a> 在泛型约束中使用类型参数</h3> <p>你可以声明一个类型参数，且它被另一个类型参数所约束。 比如，现在我们想要用属性名从对象里获取这个属性。 并且我们想要确保这个属性存在于对象 <code>obj</code> 上，因此我们需要在这两个类型之间使用约束。</p> <div class="language-typescript line-numbers-mode"><pre class="language-typescript"><code><span class="token keyword">function</span> <span class="token generic-function"><span class="token function">getProperty</span><span class="token generic class-name"><span class="token operator">&lt;</span><span class="token constant">T</span><span class="token punctuation">,</span> <span class="token constant">K</span> <span class="token keyword">extends</span> <span class="token keyword">keyof</span> <span class="token constant">T</span><span class="token operator">&gt;</span></span></span> <span class="token punctuation">(</span>obj<span class="token operator">:</span> <span class="token constant">T</span><span class="token punctuation">,</span> key<span class="token operator">:</span> <span class="token constant">K</span> <span class="token punctuation">)</span> <span class="token punctuation">{</span>
  <span class="token keyword">return</span> obj<span class="token punctuation">[</span>key<span class="token punctuation">]</span>
<span class="token punctuation">}</span>

<span class="token keyword">let</span> x <span class="token operator">=</span> <span class="token punctuation">{</span>a<span class="token operator">:</span> <span class="token number">1</span><span class="token punctuation">,</span> b<span class="token operator">:</span> <span class="token number">2</span><span class="token punctuation">,</span> c<span class="token operator">:</span> <span class="token number">3</span><span class="token punctuation">,</span> d<span class="token operator">:</span> <span class="token number">4</span><span class="token punctuation">}</span>

<span class="token function">getProperty</span><span class="token punctuation">(</span>x<span class="token punctuation">,</span> <span class="token string">'a'</span><span class="token punctuation">)</span> <span class="token comment">// okay</span>
<span class="token function">getProperty</span><span class="token punctuation">(</span>x<span class="token punctuation">,</span> <span class="token string">'m'</span><span class="token punctuation">)</span> <span class="token comment">// error</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br></div></div></div></div> <div class="page-slot page-slot-bottom"><!-- 横向自适应 -->
      <ins class="adsbygoogle"
          style="display:block"
          data-ad-client="ca-pub-7828333725993554"
          data-ad-slot="6620245489"
          data-ad-format="auto"
          data-full-width-responsive="true"></ins>
      <script>
          (adsbygoogle = window.adsbygoogle || []).push({});
      </script></div> <div class="page-edit"><!----> <div class="tags"><a href="/tags/?tag=TypeScript" title="标签">#TypeScript</a></div> <!----></div> <div class="page-nav-wapper"><div class="page-nav-centre-wrap"><a href="/pages/870a51ba2a9edfad/" class="page-nav-centre page-nav-centre-prev"><div class="tooltip">函数</div></a> <a href="/pages/7279420c899c505d/" class="page-nav-centre page-nav-centre-next"><div class="tooltip">类型推断</div></a></div> <div class="page-nav"><p class="inner"><span class="prev">
        ←
        <a href="/pages/870a51ba2a9edfad/" class="prev">函数</a></span> <span class="next"><a href="/pages/7279420c899c505d/">类型推断</a>→
      </span></p></div></div></div> <div class="article-list"><div class="article-title"><a href="/archives/" class="iconfont icon-bi">最近更新</a></div> <div class="article-wrapper"><dl><dd>01</dd> <dt><a href="/pages/dcedab/"><div>Nginx配置https转http</div></a> <span>12-10</span></dt></dl><dl><dd>02</dd> <dt><a href="/pages/82baa3/"><div>使用State Hook</div></a> <span>04-06</span></dt></dl><dl><dd>03</dd> <dt><a href="/pages/72710d/"><div>使用Effect Hook</div></a> <span>04-06</span></dt></dl> <dl><dd></dd> <dt><a href="/archives/" class="more">更多文章&gt;</a></dt></dl></div></div></main></div> <div class="footer"><!----> 
  Theme by
  <a href="https://github.com/xugaoyi/vuepress-theme-vdoing" target="_blank" title="本站主题">Vdoing</a> 
    | Copyright © 2021-2022
    <span><div style="width:300px;margin:0 auto; padding:20px 0;"><a target="_blank" href="http://www.beian.gov.cn/portal/registerSystemInfo?recordcode=13019902000398" style="display:inline-block;text-decoration:none;height:20px;line-height:20px;"><img src="" style="float:left;"/><p style="float:left;height:20px;line-height:20px;margin: 0px 0px 0px 5px; color:#939393;">冀公网安备 13019902000398号</p></a></div></span></div> <div class="buttons"><div title="返回顶部" class="button blur go-to-top iconfont icon-fanhuidingbu" style="display:none;"></div> <div title="去评论" class="button blur go-to-comment iconfont icon-pinglun" style="display:none;"></div> <div title="主题模式" class="button blur theme-mode-but iconfont icon-zhuti"><ul class="select-box" style="display:none;"><li class="iconfont icon-zidong">
          跟随系统
        </li><li class="iconfont icon-rijianmoshi">
          浅色模式
        </li><li class="iconfont icon-yejianmoshi">
          深色模式
        </li><li class="iconfont icon-yuedu">
          阅读模式
        </li></ul></div></div> <div class="body-bg" style="background:url() center center / cover no-repeat;opacity:0.5;"></div> <!----> <div class="custom-html-window custom-html-window-rb" style="display:;"><div class="custom-wrapper"><i class="close-but">×</i> <div><!-- 固定160*160px -->
      <ins class="adsbygoogle"
          style="display:inline-block;max-width:160px;max-height:160px"
          data-ad-client="ca-pub-7828333725993554"
          data-ad-slot="8377369658"></ins>
      <script>
          (adsbygoogle = window.adsbygoogle || []).push({});
      </script>
      </div></div></div></div><div class="global-ui"></div></div>
    <script src="/assets/js/app.ae5bf724.js" defer></script><script src="/assets/js/2.72b09a26.js" defer></script><script src="/assets/js/3.96877024.js" defer></script><script src="/assets/js/165.08b51ce6.js" defer></script>
  </body>
</html>